Writing instruments, and specifically pencils, have been in widespread use for hundreds of years, with mechanical pencils dating as far back as the 18th century. The first eraser was mounted on the end of a pencil in the late 1800s and by the 1920s, almost all of the pencils sold in America included erasers. Over that time, various iterations of stand-alone, removable, and integrated erasers have been developed for use with various pencils and other writing instruments. Notably, mechanical pencils adopted the use of extendable erasers, to increase the volume of eraser available with each writing instrument, and to allow for the use of user-replaceable erasers. A number of actuation or actuation mechanisms for exposing the eraser are known in the art.
One common method of actuating an eraser from an end of a writing instrument is a twist-type actuation mechanism in which the user twists a rotating knob in one direction to extend the eraser from the eraser end of the writing instrument, and twists the knob in the opposite direction to withdraw the eraser back into the eraser end. Conventional twist-to-extend mechanisms generally allow for the free rotation of the eraser knob in either direction. When the eraser is used, pressure is applied to the writing instrument to create the friction needed between the writing instrument, eraser, and the writing substrate to allow the eraser to erase marks from the substrate. These extendable erasers are frequently prone to unintended retraction, specifically, when the extended eraser is used, the applied pressure can cause the actuation mechanism to rotate and result in the retraction of the eraser. Alternatively, it may result in inadvertent extension of the eraser, which can lead to breakage of the eraser if it is over extended. Both conditions are undesirable and disadvantageously interrupt the erasing operation.
Accordingly, a need exists to create a simple, reliable, eraser retraction and actuation mechanism that overcomes the one or more of the disadvantages of current designs.